1. Field of the Invention
The present invention relates to an output control apparatus for an internal combustion engine of a motor vehicle equipped with a transmission, which apparatus is destined for controlling electrically an opening degree of a throttle valve for thereby regulating an amount or flow rate of intake air supplied to the engine by means of a throttle actuator. More particularly, the present invention is concerned with an engine power control apparatus for a motor vehicle, which apparatus can prevent sudden start of a motor vehicle and a shift shock which is likely to occur when the transmission is shifted from a neutral range (inclusive of a parking range) to a drive range (inclusive of a reverse range), to thereby enhance drivability of the motor vehicle substantially independent of the shift operation of the transmission.
2. Description of Related Art
For having better understanding of the invention, background techniques thereof will first be reviewed in some detail. FIG. 8 is a block diagram showing schematically a hitherto known or conventional output power control apparatus for an internal combustion engine of a motor vehicle, as disclosed, for example, in Japanese Unexamined Patent Application Publication No. 14181/1991 JP-A-3-14181. In the figure, reference numeral 1 designates an accelerator pedal actuated by a driver for acceleration of an internal combustion engine and hence a motor vehicle equipped with the engine.
There are provided in association with the accelerator pedal 1, an accelerator sensor 2 and an accelerator switch 3, wherein the accelerator sensor 2 serves for detecting the accelerator pedal actuation quantities .alpha.1 and .alpha.2 (opening degree of a throttle valve) corresponding to the accelerator pedal depression strokes, respectively, while the accelerator switch 3 serves for detecting whether the accelerator pedal 1 is actuated or not.
The accelerator sensor 2 is comprised of a first accelerator sensor element 2a for detecting the first accelerator pedal actuation quantity .alpha.1 and a second accelerator sensor element 2b for detecting the second accelerator pedal actuation quantity .alpha.2. Further, the accelerator switch 3 serves also as an idle switch and outputs an idle signal A when the accelerator pedal 1 is not actuated.
On the other hand, the motor vehicle is equipped with a vehicle speed sensor 4 for detecting a vehicle speed V, a main switch 5 for outputting a start signal B indicating the start of the motor vehicle which is put into operation when the switch 5 is closed by the driver, and an internal combustion engine (hereinafter also referred to simply as the engine) 6 for generating power or torque for driving the motor vehicle.
The engine 6 is provided with an intake pipe 7 for supplying intake air to the engine 6. On the other hand, the intake pipe 7 is provided with a throttle valve 8 for regulating the flow rate of the intake air supplied to the engine 6, and a throttle actuator 9 for adjusting the opening degree .theta. of the throttle valve 8 (hereinafter also referred to as the throttle opening degree .theta.).
Further provided in association with the intake pipe 7 is a throttle position sensor 10 for detecting the opening degree .theta. of the throttle valve. On the other hand, provided in association with the engine 6 are a rotation speed sensor 11 for detecting the engine rotation number Ne (rpm) and a water temperature sensor 12 for detecting the water temperature TW of engine cooling water. The signal outputted from the water temperature sensor 12 and indicating the temperature of cooling water is used for the engine control as described hereinafter.
The engine 6 has an output shaft to which a transmission 13 is operatively coupled for transmitting output torque to the driving wheels of the motor vehicle. Provided in association with the transmission 13 is a shift range detecting switch 14 for detecting shift information SR of the transmission 13. Parenthetically, it should be mentioned that an oil temperature sensor (not shown) is provided for detecting oil temperature of the transmission 13, wherein the output signal of the oil temperature sensor can be utilized also as temperature information similarly to the water temperature TW of the engine 6.
Of the various sensor signals or information, the vehicle speed V, the engine rotation number Ne (rpm), the water temperature TW (or oil temperature of the transmission 13), the shift information SR and the accelerator pedal actuation quantity .alpha. can provide information concerning the load state of the engine 6.
A throttle control means 15 for controlling the throttle actuator 9 may be constituted by a microcomputer and an electronic control unit (also referred to as the ECU in abbreviation) which incorporates a memory.
The throttle control means 15 is designed to arithmetically determine a control quantity C on the basis of various sensor information such as the accelerator pedal actuation quantity .alpha., the idle signal A, the vehicle speed V, the start signal B, the throttle opening degree .theta., the engine rotation number Ne (rpm), the water temperature TW and the shift information SR.
More specifically, the throttle control means 15 is so designed as to arithmetically determine the desired throttle opening degree .theta.o of the throttle valve 8 on the basis of the load information including at least the shift information SR and the accelerator pedal actuation quantity .theta. in accordance with a program stored previously in the memory by using data also stored therein, to thereby set a control quantity C for the throttle actuator 9 on the basis of deviation or difference .DELTA..theta. between a detected throttle opening degree .theta. and a desired throttle opening degree .theta.o (.DELTA..theta.=.theta.o-.theta.).
In other words, the throttle control means 15 sets the control quantity C such that the throttle opening degree .theta. coincides with the desired throttle opening degree .theta.o so that the deviation .DELTA..theta. becomes zero, to thereby control electrically the throttle actuator 9 on the basis of the control quantity C.
Now, description will turn to operations of the conventional control apparatus shown in FIG. 8.
When the operator or driver closes the main switch 5 by inserting key into a key slot for starting the motor vehicle, a starter motor (not shown) is electrically energized, and at the same time the start signal B is generated, in response to which the throttle control means 15 is actuated.
At this time point, however, the accelerator pedal 1 is not yet operated. Consequently, the idle signal A is generated by the accelerator switch 3. Further, the throttle valve 8 is fully closed.
Consequently, the throttle control means 15 supplies to the throttle actuator 9 a signal indicative of the control quantity C which corresponds to the desired throttle opening degree .theta.o when the starter motor is to be started in the state where the throttle valve 8 is fully closed.
In response, the throttle actuator 9 moves the throttle valve 8 installed within the intake pipe 7 to a position corresponding to the desired throttle opening degree .theta.o from the fully closed position to thereby allow an amount of intake air demanded for starting the motor vehicle supplied to the engine 6. Thus, operation of the engine 6 can be started.
Subsequently, when the driver depresses the accelerator pedal 1 in order to accelerate the motor vehicle, the throttle control means 15 responds thereto by determining arithmetically the desired throttle opening degree .theta.o corresponding to the accelerator pedal actuation quantity (depression stroke) .alpha. derived from the output of the accelerator sensor 2.
Further, the throttle control means 15 arithmetically determines deviation or difference .DELTA..theta. between the desired throttle opening degree .theta.o and the detected throttle opening degree .theta. to thereby supply to the throttle actuator 9 a signal indicating the control quantity C which can make the deviation .DELTA..theta. zero.
Thus, the throttle actuator 9 is supplied with an electric power conforming to the control quantity C from an on-board battery (not shown) to drive the throttle valve 8 until the throttle opening degree .theta. coincides with the desired throttle opening degree .theta.o.
Further, when speed change gear position is changed by the driver from a neutral range (hereinafter referred to as the N range inclusive of the parking range) to a driver (hereinafter referred to as the D range inclusive of a reverse range) through shift operation of the transmission 13 operatively coupled to the engine 6, the shift range detecting switch 14 outputs a signal indicating the shift information SR.
Then, the throttle control means 15 discriminatively decides the load-increased state of the transmission 13 on the basis of the shift information SR to determine arithmetically the control quantity C which is so corrected as to increase the desired throttle opening degree .theta.o by a proper value for preventing the engine rotation number Ne (rpm) from lowering due to increase of the load applied to the transmission 13.
In this conjunction, it is however noted that a delay time td is involved until the speed-change gear position to which the transmission 13 is shifted through the above-mentioned shift operation becomes actually effective, as is known in the art.
Consequently, before the delay time td has lapsed, there may arise such situation in which the incremental correction of the throttle opening degree .theta. continues to be carried out by the throttle control means 15, as a result of which the throttle opening degree .theta. is corrected in excess and hence the engine rotation number Ne (rpm) increases excessively, providing a cause for a sudden or abrupt start of the motor vehicle or occurrence of remarkable shock applied to the driver, to disadvantage. Hereinafter, the shock which may occur upon shift operation of the transmission will be referred to as the shift shock.
FIGS. 9 and 10 are timing charts for illustrating operations of the conventional output power control apparatus for the internal combustion engine of a motor vehicle, wherein FIG. 9 is depicted on the presumption that the transmission is shifted from the N range to the D range with the throttle valve being held in the fully closed state, while FIG. 10 is depicted on the assumption that the accelerator pedal actuation quantity .alpha. increases immediately after the shift of the transmission from the N range to the D range.
Referring to FIG. 9, the throttle opening degree .theta. increases immediately in response to the transmission shift information SR indicating the shift to the D range from the N range.
Consequently, immediately in succession to the shift operation of the transmission 13, the state in which the throttle opening degree .theta. is corrected in excess prevails over a period corresponding to the delay time td involved before the shifted position of the transmission 13 becomes effective, as a result of which the engine rotation number Ne (rpm) increases remarkably.
For this reason, shock of large magnitude will occur upon shift manipulation of the transmission 13, being accompanied with sudden start of the motor vehicle.
Referring to FIG. 10, when the accelerator pedal 1 is depressed immediately after the shift of the transmission 13 from the N range to the D range, the throttle opening degree .theta. increases further in response to the increase of the accelerator pedal actuation quantity .alpha..
Consequently, the engine rotation number Ne (rpm) increases further, which in turn means that shock due to the shift manipulation increases while the speed of the motor vehicle becomes more likely to increase abruptly.
As will be appreciated from the foregoing, in the conventional output power control apparatus for the internal combustion engine of the motor vehicle, the throttle opening degree .theta. is corrected incrementally in response to the shift information SR generated upon shift manipulation of the transmission 13 from the N range to the D range, as a result of which the throttle opening degree .theta. is corrected in excess over the period corresponding to the delay time td inherent to the transmission 13. Consequently, abrupt start of the motor vehicle as well as the so-called shift shock of remarkably large magnitude will be incurred. Thus, drivability of the motor vehicle is degraded upon shift manipulation, to a disadvantage.
In particular, when the accelerator pedal 1 is depressed after the transmission 13 is shifted from the N range to the D range, the throttle opening degree .theta. increases further, whereby the sudden start of the motor vehicle is more likely to occur.